Spatial and statistical analyses of parameters influencing arsenic distribution in the lowland Drava River area, northeastern Croatia

Soils with elevated arsenic contents are common in the Pannonian Basin. However, little is known about their distribution and occurrence. The subject of this study is the distribution of arsenic in Gleysol developed on an agricultural field in the Podravina region, Croatia. The main objective was to determine which soil parameter has the greatest influence on the overall distribution of arsenic in the area. Mineralogical, geochemical, and physico-chemical characteristics of 56 topsoil samples in were analyzed with statistical analyses, and the spatial distribution of the most important soil parameters was determined and presented. Mineralogical analysis revealed the presence of quartz, plagioclase, clays and micas, and Fe-oxyhydroxide goethite. Geochemical analysis determined elevated contents of iron (max. 23.37 mass. %) and arsenic (max. 824 mg/kg). The spatial distribution of eight parameters indicates overlap in the distribution of iron and arsenic, influenced by the topography of the area. The hierarchical cluster analysis resulted in two main groups: Fe-rich samples (Group 1) and Si-rich samples (Group 2). The Si-rich group of samples has lower arsenic contents, while the Fe-rich group has elevated arsenic contents. This indicates that iron content is the parameter that has the largest influence on the overall distribution of As. Although Fe-oxides can be dissolved under reductive conditions, the predominant presence of well-crystalized goethite implies that As is not mobilized under reductive conditions and remains adsorbed onto goethite mineral phase.